Liquid nitrogen is extremely cold and therefore potentially hazardous. The warm laboratory dewar, funnel, and detector may cause the liquid nitrogen to boil rapidly and spatter. When filling the detector dewar, be careful not to contact the liquid nitrogen with your skin.
Always wear protective gloves and splash-proof goggles when refilling the liquid nitrogen dewar. Follow precautions described in the material safety data sheets provided by your liquid nitrogen vendor.
Use proper ventilation when refilling the liquid nitrogen dewar. Gases formed as liquid nitrogen boils off can create an oxygen deficient atmosphere in an insufficiently ventilated room.